1. Technical Field of the Invention
The present invention relates to a magnetic bearing control device for controlling a magnetic bearing that supports a rotor effecting high speed rotation such as TMP (Turbo Molecular Pump) in non-contact manner in a state of magnetic levitation.
2. Related Art
Generally, a magnetic bearing for supporting a rotor in non-contact manner is known as a bearing for the rotor effecting high speed rotation. A device using such magnetic bearing is a Turbo Molecular Pump (hereinafter referred to as xe2x80x9cTMPxe2x80x9d) used in the semiconductor manufacturing devices, for example. This Turbo Molecular Pump typically has a machine main body (pump main body) for supporting a rotation body (rotor) constituting a pump with a control type magnetic bearing in non-contact manner and rotating it with a motor, and a controller (magnetic bearing control device) for controlling the machine main body.
In the related magnetic bearing control device for TMP, a DSP (Digital Signal Processor) constituting a control unit is usually employed to control the magnetic bearing and an inverter for driving the motor independently of each other (e.g., see JP-A-2000-18245).
Specifically, in the related magnetic bearing control device for TMP, the DSP as a magnetic bearding drive controller outputs an electromagnet control signal for controlling the electromagnets of the magnetic bearing so as to control the magnetic bearing to move the rotor from a touch down bearing up to a predetermined target position in magnetic levitation and support it in non-contact manner. Also, the DSP as an inverter controller outputs a revolution number instruction signal for the motor to the inverter, and the inverter controls the motor to drive and rotate the rotor at a desired number of revolutions based on the revolution number instruction signal. The number of revolutions of the motor is controlled by the inverter so that the rotor maybe rotated at a maximum permissible number of revolutions or less.
However, in the related magnetic bearing control device for TMP as described above, when the number of revolutions cannot be controlled due to a malfunction in the inverter or the DSP caused by the noise, for example, there is the fear that the rotor may be rotated beyond the maximum permissible rotation, causing a centrifugal breakage. Further, there is the fear that an over-current may be supplied to the windings of the motor from the inverter, causing a burning of the windings or a thermal breakage due to rise in temperature of the inverter.
Also, in some of the related magnetic bearing control devices for TMP, a malfunction detection device is provided, as disclosed in JP-A-11-22729, for example. Such related magnetic bearing control devices for TMP controls the inverter or the magnetic bearing in accordance with a malfunction determined by the DSP, when the malfunction is detected by the malfunction detection device. More specifically, when a malfunction such as an abnormal rise in temperature of the inverter or an over-current of the motor is detected, the DSP shut down the supply of electric power from the inverter to the motor for enabling the inverter to effect a so-called free run control for rotating the rotor by inertia, thereby protecting the inverter and the motor. Also, when a malfunction such as an abnormal operation of the magnetic bearing or a power failure is detected, the DSP controls the inverter to brake the motor and stop the rotor promptly.
However, when the inverter itself get out of order and became uncontrollable, or the DSP break down and cannot control the inverter, the related magnetic bearing control device for TMP can not stop the rotational operation of the motor and the rotor, and prevent occurrence of the breakdown of the control object devices such as a centrifugal breakage of the rotor or a burning of the motor windings due to over-current, and the breakdown of the inverter within the control device.
In the light of the above-mentioned problems associated with the related art, it is an object of the present invention to provide a magnetic bearing control device which is capable of preventing the breakdown of the control object devices such as a rotor and the control device by securely stopping the rotational drive of the rotor by a motor, even when a malfunction occurs in an inverter for driving and controlling the motor.
According to the present invention, there is provided a magnetic bearing control device for controlling a magnetic bearing for supporting a rotor in non-contact manner, and a motor for rotating the rotor and capable of generating an electric power with the rotation of the rotor, comprising:
a magnetic bearing drive controller which drives and controls the magnetic bearing;
a motor drive circuit including an inverter for driving the motor, a regenerative circuit for supplying a regenerative electric power generated by the motor to the magnetic bearing drive controller, and a switch portion for selectively switching the connection of the inverter and the regenerative circuit to the motor;
an inverter controller which controls the inverter; and
an over-speed detection circuit for detecting a number of revolutions of the rotor and outputting an over-speed detection signal when the detected number of revolutions is greater than or equal to a preset number of revolutions,
wherein the motor drive circuit performs a switching operation of the switch portion to separate the inverter from the motor, and connect the regenerative circuit to the motor, when the over-speed detection signal from the over-speed detection circuit is input.
In the magnetic beating control device as constituted above, when the motor drive circuit performs a switching operation of the switch portion to separate the inverter from the motor, when an over-speed detection signal is input from the over-speed detection circuit. Hence, irrespective of the states of the inverter for driving and controlling the motor and the inverter controller, the motor and the rotor can be securely stopped by shutting off the electric power from the inverter to the motor. Further, since the motor and the regenerative circuit can be connected by the switching operation, the rotor can be stopped promptly by employing a regenerative electric power of the motor that is supplied via the regenerative circuit to the magnetic bearing drive controller, as the magnetic bearing driving power.
Further, according to the invention, there is provided the magnetic bearing control device as described above, further comprising a power failure detection circuit for detecting a power failure, which is connected between the over-speed detection circuit and the motor drive circuit, wherein the power failure detection circuit outputs a switching signal of the switch portion to the motor drive circuit for separating the inverter from the motor, and connect the regenerative circuit to the motor, when the power failure is detected or an over-speed detection signal is input from the over-speed detection circuit.